This invention relates to hydraulic fuses of the type that pass a system's maximum flow with acceptable pressure loss and which closes in response to a fluid flow which exceeds a predetermined maximum flow.
The fluid fuse of the present invention closes in response to either a gradual increase in fluid flow to a trigger flow rate or a sudden increase in fluid flow upon failure of a fluid conduit or other component of a system with which the fluid fuse is associated. To obtain the desired performance, the lowering of the trigger flow due to the variation of liquid viscosity, or due to external effects such as shock and vibration must not reduce the trigger flow to or below the system maximum flow. The allowable lowering of the trigger flow is dependent on the difference between the mean value of the trigger flow and the system maximum flow. By way of example, if the mean value of the trigger flow is 20 percent above the system maximum flow, the deviation of trigger flow from the mean must be less than 20 percent of the system maximum flow. It is therefore of advantage to utilize a high difference between the mean trigger flow and the system maximum flow and to minimize the effects of viscosity, shock and vibration.
In the related prior art, Jackson U.S. Pat. No. 3,741,241 employs a shut-off device that is biased open by a spring and is driven closed by the pressure drop across the closure device, and Tilman U.S. Pat. No. 3,476,141 and Waterman U.S. Pat. No. 2,821,209 employ a fixed orifice in series with the shut-off device. In both Tilman and Waterman the pressure drop across the fixed orifice produces principally the same force as does the pressure drop across the shut-off device and accordingly, these fuses would be viscosity sensitive even if the fixed orifice were made viscosity insensitive. The viscosity variation encountered in normal liquid service could cause the shut-off flow of these fuses to vary by a factor of greater than 100.